Impeller-stator combination for aeration machines



Feb. 28, 1961 c. M. ANDERSON ETAL 2,973,095

IMPELLER-STATOR COMBINATION FOR AERATION MACHINES Filed July 9, 1957 2 Sheets-Sheet 2 INVENTOR. CHARLES M. ANDERSON MARSHALL J. $AYERS ATTORNEYS 2,973,095 IMPELLER-STATOR COMBINATION FOR AERATION MACHINES Charles M. Anderson and Marshall J. Sayers, Salt Lake City, Utah, assignors to The Galigher Company, Salt Lake City, Utah, a corporation of Utah Filed July 9, 1957, Ser. No. 670,688

3 Claims. (Cl. 209-469) This invention relates to aeration machines of a type intended primarily for flotation purposes in the separation of diverse solid particles contained in an aqueous pulp.

Machines of this type are especially useful in the metallurgical field for aerating ore pulps in the a plication of flotation processes thereto for the separation of mineral values from the gangue content of sucn pulps.

In a flotation operation, an aqueous pulp of the particles to be separated is subjected to aeration in the presence of suitable reagents. Most commercially used flotation machines are of so-called sub-aeration type, wherein air is introduced into the pulp coincidentally with vigorous agitation of such pulp by means of a submerged impeller.

Mechanical devices for agitating and aerating aqueous pulps in flotation cells have been developed in great profusion. Yet, conditions necessary for the obtaining of maximum recoveries of valuable particles from a pulp, as against unwanted particles thereof, and for achieving clean separation between several valued components of a flotation pulp, are so exacting that throughout the history of the flotation art there have been and currently are constant efforts to improve the operation of flotation machines.

A particular type of machine which has achieved widespread use throughout the industry is illustrated and described in US. Patents No. 2,055,065, No. 2,085,947, and No. 2,182,442, granted to Lionel E. Booth under dates of September 22, 1936, July 6, 1937, and December 5, 1939, respectively.

The first of these patents discloses, in combination with a flotation cell, a circular impeller having a closed top and a multitude of elongate fingers or teeth depending from the outer periphery of such top in mutually spaced relationship. The second is concerned with an improvement for effecting increased aeration, wherein a stationary peeler blade structure encircles an impeller corresponding to that of the first patent, for coaction therewith in establishing advantageous bubble column conditions in the flotation cell. The bubble column of any flotation cell, it should be noted, is the effective working agency in carrying out the flotation process.

While the teachings of the above patents have been of considerable importance in commercial flotation practice as embodied in the well known Agitair flotation machine produced by The Galigher Company of Salt Lake City, Utah, and have led to certain modifications and improvements as set forth in US. Patents No. 2,673,724 and No. 2,767,964, issued March 30, 1954 and October 23, 1956, respectively, to John T. Potts for Impeller for Flotation Machines" and Impeller-Stator Combination for Flotation Machines, respectively, work has continued toward the achievement of even more effective results in practice.

The effectiveness of the bubble column of any flotation machine is largely determined by the size of the bubbles produced in the pulp by the aerating action of the machine. Given sufficient aeration to produce a proper volume of froth in any given instance, it usually holds true that the smaller the size of the bubbles the greater the recovery of particles to be floated.

2,973,095 Patented Feb. 28, 19 61 It is an object of this invention to achieve more effective aeration than heretofore with sub-aeration types of flotation machines, particularly the Booth and the Potts machines of the several patents referred to hereinbefore, by reducing the size of the bubbles produced by the agitating and aerating components of such machines and by otherwise effecting greater dissemination of the air in the pulp.

This object is attained by a novel impeller-stator combination wherein a stator is disposed within the impeller in operative relationship with the air-disseminating members of the latter. Such stator serves to break up the flow of both air and pulp within the impeller and to bring about an effective initial dissemination of air in the pulp prior to discharge of air and pulp by the impeller.

The combination has proven especially effective-when the impeller is of the Booth or Potts type utilized in the aforesaid Agitair flotation machine, that is to say, when it comprises a series of closely spaced fingers de pending from the circular outer periphery of a disc or similar top member of the impeller, and has proven even more effective in combination with such an impeller and the peeler blade stator structure of the Booth and Potts patents.

It is presently preferred to form the stator that is disposed within the impeller, i.e. the inner stator, of a series of closely spaced upstanding fingers similar in formation and spacing to the depending fingers of the impeller.

Further objects and features of the invention will become apparent from the following detailed description of the presently preferred embodiment illustrated in the accompanying drawings.

In the drawings:

Fig. 1 represents a central vertical section taken through a flotation cell of conventional type but embody ing a preferred form of the impeller-stator combination of the invention; M

Fig. 2, a horizontal section taken along the line 22 of Fig. 1 and drawn to a considerably enlarged scale;

Fig. 3, a vertical section taken along the line 3-3 of Fig. 2, the impeller shaft being eliminated;

Fig. 4, a perspective view of the inner stator per se;

Fig. 5, a vertical section taken along the line 5-5 of Fig. 2, and drawn somewhat schematically to a scale considerably enlarged over the foregoing figures, arrows being applied to indicate air and pulp flow patterns in general;

Fig. 6, a fragmentary portion of Fig. 2 drawn to an enlarged scale, arrows being applied as in Fig. 5 to indicate material flow patterns;

Fig. 7, a fragmentary vertical section taken along the line 7-7 of Fig. 6; and

Fig. 8, a view corresponding to that of Fig. 2, but illustrating a different embodiment of the invention and being fragmentary in character and drawn to a considings outflow means (not shown). An impeller 13, corresponding to what is shown in the aforesaid Potts patents, is secured to the lower end of a hollow impeller shaft 14, which depends deeply into the container 11 from a rotatable suspension mounting in the usual bearing structure 15. Air under pressure is introduced within the im- 3 peller 13 through the hollow impeller shaft 14 by means of a blower (not shown) and by way of supply piping 16 in bearing structure 15, all in a manner now conventional with the Agitair" machine. The impeller and impeller shaft are rotated in the usual manner by means of an electric motor 17 and a multiple V-belt drive 18.

Encircling the impeller 13 is peeler blade structure 19, the same being supported in slightly raised position relative to the bottom 11a of the cell by means of customary leg and bracket members 20.

The peeler blade structure 19 may be of conventional type with a conventional number of blades 21, or the number of blades may be increased so that the structure conforms to the teaching of the aforementioned Potts Patent No. 2,767,964. In either event, the individual peeler blades 21 are held rigidly together in radial, mutually spaced relationship by means of frame members 22, to which they are individually rigidly attached, as by welding. Such blades extend radially inwardly of the structure a limited distance to define a space, normally circular, for receiving the impeller 13.

The impeller 13 in the embodiment shown is provided with a circular top portion 24 and a plurality of finger portions 25 depending from the outside periphery thereof. The depending finger portions 25 are disposed in mutually and closely spaced relationship to define a multiplicity of side-discharge ports 26 therebetweem The bottom of the impeller is normally entirely open.

The surfaces of impeller top portion 24 and of depending finger portions 25 are normally covered with a coating 27 of wear and corrosion resistant material, usually rubber.

The present improvement lies in the provision of a stator structure within the impeller.

In the embodiment of Figs. l-7, the inner stator 28 includes a base portion 29 of disc formation and a plurality of finger portions 30 fixedly disposed with respect to the base portionand extending upwardly therefrom in mutually spaced relationship to define a multiplicity of side-discharge ports 31 corresponding in general with those of the impeller.

Base portion 29 is conveniently cut .from steel plate, the upwardly extending finger portions 30 being atfixed thereto by welding, as indicated, see Fig. 3. Exposed surfaces of the stator structure so formed are advantageously covered, like the impeller, with a wear and corrosion resistant material, as indicated.

It will be realized that the inner stator structure may take a variety of different forms and may be fabricated in a variety of different ways without departing from the scope of the invention (see Fig. 8, for example), the important thing .being the fingers 30 or corresponding members which project deeply within the impeller and extend preferably in mutually spaced relationship to define a series of side-discharge ports which co-operate with the impeller and with the peeler blade structure or outside stator in the operation of the machine.

The utility of the inner stator structuer in combination with an impeller of the general type concerned is well shown by the somewhat schematic views of Figs. 5, 6, and 7, wherein arrows are utilized to indicate the approximate flow patterns of air and pulp and of aerated pulp.

As is seen in'Fig. 5, rotation of the impeller 13 and the accompanying centrifugal action thereof creates a suction effect internally of such impeller, which draws pulp 32 through the lower portions of inner stator ports 31 from the lower part of the container or tank 11. In passing through inner stator 28 in more or less turbulent condition, the pulp comes into intimate contact with eddy currents of air descending within such inner stator by reason of the projection of the fingers 30 thereof into, and their disturbance of, the blanket of air 33 which spreads radially across the undersurface of impeller 23 from hollow impeller shaft 14. An effective preliminary mixture of and pulp results.

The preliminarily intermixed air and pulp material is drawn through the upper portions of inner stator ports 31 into the circular path of rotation of the depending fingers 25 of impeller 13 by reason of the centrifugal force created by such impeller. This is the zone of most intense agitation and aeration, and here the preliminarily aerated pulp has considerably more air disseminated in it by an action indicated in Figs. 6 and 7.

In those figures of the drawings, the preliminarily aerated pulp is indicated 34. In flowing through the inner stator ports 31, it establishes vacuum or suction pockets 35 along the outer surfaces of the respective inner stator fingers 30. Air from the air blanket 33 is sucked downwardly into such pockets 35 as indicated in Fig. 7, where it is very effectively disseminated in the pulp by the agitating action of the impeller fingers.

The outer stator or peeler blade structure 19 is even more effective than heretofore, because of the already highly aerated nature of the pulp discharged by the impeller. As a consequence, especially fine bubble formation is achieved below the bubble columns 36 of the machine, and optimum froth conditions are easily maintained.

It should be realized, of course, that the foregoing explanation of the action of the machine is based to a certain extent on deductions arrived at following careful observations of actual operations.

In addition to the improved aerating action, there has been considerable improvement in the smoothness of the pulp surface, this being due undoubtedly to the greater dissemination of the air, which prevents surface eruptions and boiling action of the pulp.

As has been mentioned hereinbefore, the improvement constituting this invention provides several advantages in the flotation process. These include a marked increase in aeration of the pulp, accompanied by finer bubble formation and greater dispersion of air within the pulp, easier maintenance of optimum froth volume, often an increase in metallurgical recovery, and always a marked reduction in the tendency otherwise present for flotation machines to erupt large volumes of undispersed air when air introduction approaches a maximum.

Comparative performance between an Agitair machine corresponding to the present invention and one identical thereto except for the absence of the inner stator structure 28 is shown by the following typical test data derived from laboratory operation of standard size (fortyeight inch) machines on a typical flotation pulp prepared from tailings obtained from an operating lead-zinc mill:

Standard Agizair machine [Impeller peripheral speed1l00 i tJmin .1

Air in Cu. Ft. Horse- Sand Froth. Nature of Percent Per Min. power Depth, Depth, Surface Surface Required inches inches Solids 4. 63 1 a Rocking." 21.1

5.02 1% Smooth... 35.8

5. 04 1% do 36. i

With inner stator The greater froth depth shown by the machine of the invention is indicative of its superior aerating action. Visual observation of the froth showed significantly smaller bubbles than in the case of the standard machine. The increase in horsepower required is economically insignificant considering the improved operative results.

The columns' designated percent surface solids show the solids content, in terms of weight of solids to the total weight, of respective samples of the pulp taken immediately below the froth-pulp interface. The entries repre sent measures of the ability of the particular machines concerned to place solid particles in suspension in the liquid phase of a pulp and to hold them so suspended. Ordinarily, the greater the aeration of a pulp, the more diflicult it is to hold solids in suspension. However, from the test data, it will be noted that the machine of the invention achieved equal suspension at maximum aeration and superior suspension at less than maximum. Under ordinary conditions, it would be expected that suspension of solids in the pulp would drop considerably with the greater aeration shown and that there would be a corresponding increase in the tendency for the machine to sand.

The novel impeller and inner stator combination of the invention is useful for agitating and aerating purposes, for example in pulp conditioning operations, without the outer stator or peeler blade structure, although the latter or an equivalent structure appears to be necessary for flotation purposes.

While the inner stator construction of Figs. l7 is preferred for most purposes, considerable variation is possible. For example, the construction of Fig. 8 has given significantly increased aeration and smoother pulp surface to flotation machines in which it has been installed. Here, the inner stator 46 is of unitary cruciform formation comprising upstanding members 41 resembling the usual peeler blades 42 in configuration and all radiating from a common center at which the unit is attached to the bottom of the flotation cell, as by means of a bolt 43.

As few as three of the blade members 41 give useful results, though it is ordinarily best to utilize a multiplicity of such blades, the number and spacing of same depending largely upon the nature of the pulp being treated.

Whereas this invention is here illustrated and described with respect to specific embodiments thereof, it should be realized that changes may be made within the scope of the following claims, without departing from the essential contributions to the art made by the teachings hereof.

We claim:

1. In a flotation machine which includes a container for liquid to be aerated and froth overflow means, an impeller-stator combination comprising stator members fixedly mounted within said container in mutually spaced relationship defining side-discharge ports therebetween; a hollow impeller mounted for rotation within said container about a substantially vertical axis, said impeller having a substantially closed top and a peripheral series of finger members depending therefrom and defining a multiplicity of side-discharge ports; and means remote from the impeller for introducing a stream of air into the interior of said impeller axially thereof and at the underside of its said closed top while the impeller is rotating, said stator members extending within the hollow interior of the impeller into the path of air dissemination so that the side-discharge ports thereof are disposed in the line of action of the side-discharge ports of the impeller, the container being deep relative to the heights of the impeller and stator members, the impeller having an open bottom for the entry of flotation pulp from the container,

and the finger members of said impeller terminating well above the bottom of the container and the lower ends of the said side-discharge ports of the stator, so that entry of pulp into the hollow interior of the impeller takes place essentially from below.

2. The combination of claim 1, wherein the stator members and the side-discharge ports therebetween are arranged as a circular series; and the series of stator members and the series of impeller fingers are both concentric with the rotative axis of the impeller.

3. The flotation machine of claim 1, wherein the impeller is secured to the lower end of a substantially vertical impeller shaft which is hollow and serves to conduct air into the interior of the impeller.

References (Iited in the file of this patent OTHER REFERENCES Mining Engineering, December 1955, pages 1137- 1142. 

